1. Field of the Invention
The present invention relates to a magnetic memory.
2. Description of the Related Art
A magnetoresistance effect device using a magnetic film has already been used as a magnetic head or a magnetic sensor. Moreover, it is also proposed to use the magnetoresistance effect device as a magnetic memory (magnetoresistance effect memory), and the like. In the magnetic memory, a magnetic memory using a ferromagnetic tunnel junction is expected to realize a nonvolatile storage, and a writing or reading access time less than 10 nsec, reading and writing endurance exceeding 1015 times, and small cell size like DRAM.
To realize such a magnetic memory using the ferromagnetic tunnel junction, a sufficient magneto-resistance ratio is necessary. In recent years, the magnetoresistance ratio of 20% or more has been achieved in the ferromagnetic tunnel junction. Therefore, expectation of realizing such a magnetic memory is increased more and more.
For example, a ferromagnetic tunnel junction obtained by forming a thin Al film having a thickness of 0.7 nm to 2.0 nm on a ferromagnetic layer, exposing the surface of the film to an oxygen glow electric discharge or an oxygen gas to form a tunnel barrier layer of Al2O3, and further forming a ferromagnetic layer has been proposed. According to the ferromagnetic tunnel junction, the magnetoresistance ratio of 20% or more is obtained (J. Appl. Phys. 79, 4724 (1996)). Moreover, a structure of a ferromagnetic single tunnel junction has also been proposed in which one layer of a, pair of ferromagnetic layers is combined with an antiferromagnetic layer to form a magnetization pinned layer (Jpn. Pat. Appln. KOKAI Publication No. 10-1998).
As described above, in the ferromagnetic single tunnel junction, the magnetoresistance ratio of 20% or more can be obtained. However, as compared with competing memories such as FeRAM and flash memory, the magnetic memory using the ferromagnetic single tunnel junction has a problem that power consumption on writing is large.
To solve the problem, a solid magnetic memory has been proposed in which a thin film of a high permeability material is formed around a writing wiring (U.S. Pat. Nos. 5,659,499, 5,956,267, and 5,940,319, and International Patent Application No. WO00/10172). According to this magnetic memory, since the high permeability film is formed around the wiring, a current value necessary for writing information to a magnetic recording layer can efficiently be reduced. Moreover, according to the magnetic memory, since a magnetic flux generated by the current does not extend to the outside of the high permeable magnetic film, even a cross talk can be inhibited.
However, in the magnetic memory disclosed in the U.S. Pat. No. 5,659,499, a magnetic field cannot uniformly be applied to the whole recording layer of a magnetoresistance effect film. Moreover, in the magnetic memory disclosed in the U.S. Pat. Nos. 5,956,267 and 5,940,319, when a structure of the magnetic recording layer positioned between a pair of magnetization pinned layers like in a dual spin valve type double tunnel junction as described later is used, it is difficult to efficiently apply the magnetic field to the magnetic recording layer. Furthermore, the magnetic memory disclosed in the International Patent Application No. WO00/10172 has an ideal structure for applying the magnetic field to the magnetic recording layer, but it is remarkably difficult to manufacture the structure.
Moreover, in addition to the aforementioned ferromagnetic single tunnel junction, a ferromagnetic tunnel junction in which a magnetic particle is dispersed in a dielectric material, and a ferromagnetic double tunnel junction (continuous film) have also been proposed. Even in these ferromagnetic tunnel junctions, the magnetoresistance ratio of 20% or more is obtained (Phys. Rev. B 56(10), R5747 (1997)., Applied Magnetics Journal 23, 4-2 (1999), Appl. Phys. Lett. 73(19), 2829(1998)). Additionally, according to the ferromagnetic double tunnel junction, the magneto-resistance ratio generated by increasing a voltage value applied to the magnetic tunnel junctions can be prevented from decreasing in order to obtain a desired signal voltage value.
However, the ferromagnetic double tunnel junction also has a problem that the power consumption on writing is large similarly as the ferromagnetic single tunnel junction. Moreover, when the ferromagnetic double tunnel junction is used, the magnetic recording layer is held between a pair of tunnel barrier layers and a pair of magnetization pinned layers. Therefore, even when the method disclosed in the aforementioned U.S. patent is applied, an electric current magnetic field cannot efficiently act on the magnetic recording layer. That is, the magnetic memory using the ferromagnetic double tunnel junction has a problem that the power consumption on writing is remarkably large.